1. Field of the Invention
This invention is concerned with the manufacture of lubricating oils (lubes) and, in particular, with lubricating oils derived by the conversion of olefins over fresh ZSM-5 type zeolite. More particularly, this invention is directed towards the conversion of olefins over a ZSM-5 type zeolite catalyst characterized by large crystals to obtain a lubricating oil of low pour point and high V.I. (V.I. will be used herein to denote viscosity index).
2. Prior Art
The conversion of olefins over ZSM-5 type zeolites is extremely well known in the art and is the subject of many patents. Recently issued U.S. Pat. No. 4,227,992; as well as the patents mentioned therein are excellent examples of the prior art in connection with this general subject.
U.S. Pat. No. 4,126,644 discloses the conversion of a C.sub.5 -400.degree. F. liquid fraction from a Fischer-Tropsch synthesis, predominantly C.sub.5 -C.sub.10 olefins over zeolite ZSM-5 in order to produce higher boiling products, including a 650.degree. F.+ lube fraction.
U.S. Pat. No. 3,322,848 is directed towards the manufacture of high V.I., low pour point lube oils from C.sub.10 -C.sub.18 normal alpha olefins by processing over crystalline aluminosilicate zeolites other than those of the ZSM-5 type. CL BRIEF DESCRIPTION OF THE INVENTION
It has now been found that the viscosity index of lubes produced from olefins, such as propylene, over fresh hydrogen ZSM-5 type zeolites varies with the crystal size of the zeolite. V.I. is the highest over a HZSM-5 which has a micron crystal size greater than 2 microns, intermediate over a 0.1-0.5 micron size and lowest over a 0.02-0.05 micron crystal size. Thus, the novel process of this invention resides in the conversion of olefins over an ZSM-5 type zeolites having large crystals, i.e. greater than 2 microns (hereinafter referred to as "macrocrystalline ZSM-5") and recovering from the liquid product via distillation a lube fraction which has an enhanced viscosity index.
Zeolites of the ZSM-5 type useful in the novel process of this invention include ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48.